Subcutaneous implantation of a pharmaceutical dosage forms is recognized as a potentially advantageous approach to drug delivery. Contraceptive implants may currently be introduced subcutaneously which provide effective protection for several months. These dosage forms are rapidly gaining in popularity among the medical community since treatment problems arising from poor patient compliance are eliminated. Further, depending upon the design of the pharmaceutical dosage form, treatment may be localized to that portion of the body where greater concentrations of the pharmaceutical compound is required, or treatment may result in systemic delivery of the pharmaceutical compound throughout the patient.
Although several devices have been designed to aid in implanting pharmaceutical dosage forms, these generally require application of force directly to a plunger or they may suffer from a loss of tactile sensitivity. Those devices which provide a mechanical advantage, such as a lever, to assist in delivery of the dosage form are generally unwieldy due to their size and shape. Applicant presents herein, a device for implanting pharmaceutical dosage forms which provide for mechanical leveraging to implant a pharmaceutical dosage form while maintaining a high level of tactile sensitivity and compact, ergonomically designed size.
One method for the insertion of subcutaneous pharmaceutical dosage forms involves surgical implantation. In this procedure, an incision is made at the area where the implant is desired. The implant is placed within the area using forceps or a trocar. Since the size of the incision may be large enough to require suturing, experienced medical personal are generally required to implant the dosage form.
In an effort to avoid such surgical techniques, injection system have been developed to provide a means for implantation. In U.S. Pat. No. 4,576,152, a syringe shaped cylinder containing an injection nozzle is disclosed for the implantation of bone cement. The nozzle element has a nozzle tube of reduced cross-sectional area through which a ram passes to provide high pressure injection. The system requires direct pressure to be applied to the piston. That is, no mechanical leverage is used to assist in delivery of the pharmaceutical dosage form.
In U.S. Pat. No. 4,086,914, an implant injector is disclosed for the implantation of spaced implants using a plunger system contained within a sliding member. As pressure is applied to the sliding member, the plunger moves an implant out of a cannula and into position. Again, no mechanical advantage is achieved with this system.
U.S. Pat. No. 4,661,103 discloses a magazine type implant injector which uses a slotted barrel element which is slidably mounted to an integral magazine element and cannula. Each implant advances a previously loaded implant through the cannula for implantation. Although this device allows for direct contact between the finger of the operator and the implant, no mechanical advantage is realized.
U.S. Pat. Nos. 4,659,326, 4,784,640 and 4,799,921 disclose an injector and new process of delivering an implant to cattle, wherein a double acting trigger mechanism of the injector loads a retainer and implant into a needle and then injects the retainer and implant into the animal. The injector is effectively a gun having a plunger member which moves through a bore. The plunger rod is moved by the hand trigger which is mounted centrally in the gun. Because lateral movement of the implant and plunger rod is desired, the trigger mechanism is pivoted to a yoke element which is in turn pivoted to a slider and yoked to an intermediate location on a pin which extends across the gun housing. Although mechanical advantage is realized through the use of pivot points, tactile sense may be reduced due to the loss of contiguousness between the operator and the implant due to the use of the yokes.
A gun type injector capable of dispensing pellets from a magazine rotatably supported in the injector is disclosed in U.S. Pat. No. 4,673,387. This device utilizes an injector rod which passes through the magazine and moves a pellet to be injected. The injector rod moves along a generally linear path and is operatively associated with the trigger by means of two links which provide for lateral movement of the injector rod as the trigger is depressed. Once again, some loss of tactile sense may be lost due to the links between the trigger and the device.
U.S. Pat. Nos. 4,846,793 and 4,994,028 describe a device for subcutaneous implantation of a plurality of solid, elongated medicinal pellets. The device includes a needle-like, hollow cannula within which are located a plurality of medicinal implants. The cannula is attached to a hub which slides forward and backward within a barrel. The hub has a manually engagable knob thereon so that the hub and cannula may be moved easily with respect to the barrel. The thumb of one hand is used to actuate the device. An obturator, capable of telescoping during operation, extends from the rear of the barrel into the proximal end of the cannula. Once the cannula is inserted through the skin, it is moved backward by means of the thumb knob while the barrel is maintained in a fixed position so that the operator causes the implant to remain in place under the skin as the cannula is withdrawn from around the implant. Again, no mechanical advantage is achievable with this device.
In U.S. Pat. No. 4,753,636, a presterilized, packaged, subcutaneous contraception kit which comprises a cutter device for incising skin and a subcutaneous deposit mechanism in the shape of a tapered hollow body is presented. The device is placed within an incision and used for blunt dissecting prior to implantation of the contraceptive device. As the tool is retracted, a plunger is depressed and a contraceptive device is delivered to the site.
The present invention has improved the implantation techniques needed to deliver implantable pharmaceutical dosage forms to their desired location. This unique device provides an unexpectedly high degree of tactile sense such that the operator can more accurately position the pharmaceutical dosage form subcutaneously or within bone or other biological tissue without excessive damage to surrounding tissue. Further, this device allows for various levels of mechanical advantage to be used to deliver the pharmaceutical dosage form. Due to the unique design of the device, a safety mechanism is provided which assures that excessive pressure, which might inadvertently damage the patient, is avoided. The design further provides for a smaller size device than the above mentioned hand held units, resulting in greater control over pharmaceutical dosage form implantation.